1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and, more particularly, to an electrophotographic photosensitive member having a photosensitive layer containing an azo pigment of a specific structure.
2. Description of the Prior Art
In general, an organic photosensitive members having a photosensitive layer containing an organic photoconductive substance offer various advantages over inorganic photosensitive members, and various such organic photosensitive members have been proposed and used.
Typical examples of such organic photoconductive substances are: organic photoconductive polymers such ss poly-N-vinyl carbazole and polyvinyl anthracene; low-molecular organic photoconductive substances such as carbazole compounds, anthracene compounds, pyrazoline compounds, oxadiazole compounds, hydrazone compounds and polyacryl-alkane compounds; and organic pigments and dyes such as phthalocyanine pigments, azo pigments, polycyclic quinone pigments, pellyrene pigments, indigo dyes, thio-indigo dyes, and methine squalinate dyes; and so on.
On the other hand, so-called function separation type photosensitive members have been proposed in which a photosensitive layer includes a charge generating layer containing a charge generating substance and a charge transporting layer containing a charge transporting substance. Photoconductive azo pigments suitable for use as the charge generating substance in such function separation type photosensitive member are disclosed, for example, in the specifications of U.S. Pat. Nos. 4123270, 4247614, 4251613, 4251614, 4256821, 4260672 and 4293628.
Electrophotographic apparatuses such as printers are finding increasing use as output means of microcomputers and wordprocessors, and light source devices capable of emitting lights of long wavelengths, e.g., LEDs and laser diodes, are becoming popular. This has given a rise to the demand for electrophotographic photosensitive members which can effectively be used in combination with light sources emitting radiation of long wavelengths.
The output power spectrum, including the wavelength of the maximum power .lambda. max of the laser diode undesirably varies and fluctuates depending on various factors such as variation in the characteristics of individual laser diodes, ambient air temperature and rise in the temperature of the emitting junction of the diode incurred during the emission. Therefore, an electrophotographic photosensitive member is required to exhibit a flat spectral sensitivity response characteristic distribution over the entire range of emission wavelengths. Unfortunately, however, electrophotographic photosensitive members, which have been conventionally used in monochromatic or color printers, could not meet the demand for flat spectral sensitivity distribution. In order to overcome this problem, therefore, it has been necessary to take a suitable countermeasure, such as careful selection of the laser diodes, control of the laser temperature, and so forth, which poses problems such as a rise in the costs of the printers and increase in the size of the required apparatus.
The spectral sensitivity distribution can be regarded as being flat when the amount of change or variation in the sensitivity is 0 to 15%, preferably 0 to 10%, in the range of wavelength emission of laser diodes, which is generally 760 nm to 800 nm.
Japanese Patent Laid-Open Publication No. 63-264762 discloses an azo pigment which has a specific coupler component for an electrophotographic photosensitive member which is intended for use in combination with laser diodes. This electrophotographic photosensitive member, however, is still unsatisfactory in that the amount of variation in the spectral sensitivity is 25% at the smallest in the above-mentioned emission wavelength region of 760 to 800 nm.